No abstract

A method of specifying changes in the ionospheric critical frequency along a path has been developed to more accurately estimate the effect of longitudinal horizontal electron density gradients along a path on the accuracy of the calculation of ionospheric delay of GNSS signals. The transition has been made from a linear dependence to a dependence representing a second-order curve through quadratic spline interpolation. To exemplify differences between the real form of change in the critical frequency along a path and its linear representation, we assess the effect of these differences on the accuracy of the calculation of ionospheric delay. Specifying the form of horizontal gradients of the critical frequency closest to the real one is shown to be quite important.